This invention relates to a thermoplastic resin composition having excellent characteristic features in rigidity, impact resistance and moldability and to injection moldings excellent in dimensional stability formed therefrom by an injection molding method, particularly injection moldings for automobile if interior and exterior trims.
In recent years, propylene-ethylene block copolymers have been used as automobile materials from the view points of weight reduction and cost reduction. However, previous propylene-ethylene block copolymer materials are low in impact resistance; to improve the impact resistance, it has been proposed to compound into propylene-ethylene block copolymers an ethylene-propylene copolymer rubber, ethylene-xcex1-olefin copolymer rubber or the like. When an ethylene-propylene copolymer rubber, ethylene-xcex1-olefin copolymer rubber or the like is compounded, however, though the resulting composition is improved in impact strength, the composition conversely shows a lowered rigidity and deteriorated thermal properties such as heat distortion temperature, and hence has difficulties for use as automobile interior and exterior trim materials. To solve the problems, it has been proposed to compound additionally into the composition inorganic fillers, such as calcium carbonate, barium sulfate, mica, crystalline calcium silicate and talc.
For example, JP-A-51-136735 discloses a thermoplastic resin composition comprising an ethylene-block copolymer mainly based on propylene, an ethylene-propylene rubber and talc, and describes the physical properties thereof. It also describes, only in general, that styrene-butadiene rubbers can be used similarly to the ethylene-propylene rubber, but it describes nothing about the structure and state of the product obtained by melt-kneading the rubber and about the molecular weight distribution, melt flow rate, styrene content, etc. of the rubber.
JP-A-6-192,500 discloses a propylene-based resin composition comprising a propylene-ethylene block copolymer and an ethylene-1-hexene copolymer. It further describes as additional compounding ingredients, the blend of talc or the like, which are auxiliary additive components conventionally used in the process for producing resin compositions, and styrene-butadiene type rubbers or the like. However, it describes nothing about the structure and state of the product obtained by melt-kneading the rubber and about the molecular weight distribution, melt flow rate, styrene content, etc. of the rubber.
JP-A-6-192506 discloses a polypropylene composition comprising polypropylene, ethylene-1-octene random copolymer and talc, but it describes nothing of the use of vinyl aromatic compound-containing rubbers.
As described above, previous resin compositions comprising a propylene-ethylene block copolymer, ethylene-propylene copolymer rubber or ethylene-xcex1-olefin copolymer rubber and inorganic filler have been, as automobile interior and exterior trim materials, still insufficient in the balance of impact strength with rigidity and in injection moldability. Further, prior technologies for using styrene-butadiene type rubbers or the like have also been unsatisfactory.
Under such circumstances, the object of this invention is to provide a polypropylene-based resin composition comprising a crystalline polypropylene-based resin, elastomer and talc which satisfies, in respect of physical properties, the impact resistance and rigidity required for automobile interior and exterior trim materials and is excellent in injection moldability and to provide injection moldings thereof, particularly injection moldings for automobile interior and exterior trim uses.
The present inventors have found that a polypropylene-based resin composition and injection moldings thereof which can meet the above-mentioned objects can be obtained by using a specific crystalline polypropylene-based resin as the main component and melt-kneading therewith, in specific compounding ratios, a specific elastomer component and talc, and resultantly attained this invention.
Thus, this invention relates to a thermoplastic resin composition which is obtained by melt-kneading a mixture comprising (1) 55-75% by weight of a crystalline polypropylene-based resin, (2) 10-30% by weight of an elastomer comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing-rubber and an ethylene-xcex1-olefin random copolymer rubber and (c) 15-25% by weight of talc having an average particle diameter of not more than 3 xcexcm, and which satisfies the following conditions (a)-(c):
(a) when the crystalline polypropylene-based resin (1) has been melt-kneaded with the elastomer (2) comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-a-olefin random copolymer rubber, the long period obtained by small angle X-ray scattering attributable to the vinyl aromatic compound-containing rubber is 12-24 nm,
(b) when the crystalline polypropylene-based resin (1) has been melt-kneaded with the elastomer (2) comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-xcex1-olefin random copolymer rubber, elastomer particles which undergo micro phase separation to have the form of particle, and are present in the vicinity of the interface between particles of the elastomer and the crystalline polypropylene-based resin as matrix, have a particle diameter of not more than 30 nm, and
(c) the difference between the glass transition point (Tg1) assigned to the crystalline propylene homopolymer portion of the crystalline polypropylene-based resin (1) and the glass transition point (Tg2) assigned to the crystalline propylene homopolymer portion of a composition obtained by melt-kneading the crystalline polypropylene-based resin (1) with the elastomer (2) comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-xcex1-olefin random copolymer rubber and talc (3) (that is, xcex94Tg=Tg1xe2x88x92Tg2) is 4.0-7.0xc2x0 C.
This invention also relates to injection moldings formed from the above-mentioned polypropylene-based resin composition by an injection molding method.
This invention further relates to injection moldings for automobile interior and exterior trim uses.
This invention is described in detail below.
The thermoplastic resin composition of this invention is a composition obtained by melt-kneading a mixture comprising (1) 55-75% by weight of a crystalline polypropylene-based resin, (2) 10-30% by weight of an elastomer comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-xcex1-olefin random copolymer rubber and (3) 15-25% by weight of talc having an average particle diameter of not more than 3 xcexcm.
The crystalline polypropylene-based resin (1) used in this invention is not particularly limited so long as it is crystalline and may be, for example, propylene homopolymers, propylene-ethylene copolymers and propylene-xcex1-olefin copolymers. The xcex1-olefin in the copolymer has at least 4 carbon atoms and may be, for example, butene, pentene, hexene, heptene, octene, decene and the like.
Particularly preferably used crystalline polypropylene-based resin (1) is a crystalline polypropylene selected from a crystalline ethylene-propylene block copolymer (1A) or a mixture (1B) of the crystalline ethylene-propylene block copolymer (1A) with a crystalline propylene homopolymer.
The crystalline ethylene-propylene block copolymer (1A) herein referred to is a crystalline ethylene-propylene block copolymer consisting essentially of a propylene homopolymer portion (hereinafter referred to as the first segment) and an ethylene-propylene random copolymer portion (hereinafter referred to as the second segment).
The propylene homopolymer portion, which is the first segment, has a Q value of preferably 3.0-5.0, more preferably 3.5-4.5, which value is the weight average molecular weight (Mw)/number average molecular weight (Mn) ratio determined by the gel permeation chromatography (GPC) method. Further, the portion has an isotactic pentad fraction of preferably not less than 0.98, more preferably not less than 0.99, as calculated from its 13C-NMR, and has an intrinsic viscosity [xcex7]p of preferably 0.7-1.1 dl/g, more fit preferably 0.8-1.0 dl/g as measured in tetralin solution at 135xc2x0 C.
When the Q value of the propylene homopolymer portion of the first segment is less than 3.0, the fluidity tends to be poor, and when the Q value exceeds 5.0, a good result cannot be obtained in the balance of rigidity with impact resistance in some cases. Further, when the isotactic pentad fraction of the portion is less than 0.98, it is difficult to attain the intended rigidity, heat resistance and the like in some cases. When the intrinsic viscosity [xcex7]p of the portion is less than 0.7 dl/g the impact strength tends to be low, and when it exceeds 1.1 dl/g, the fluidity tends to deteriorate.
The ethylene-propylene random copolymer portion of the second segment has an intrinsic viscosity [xcex7]EP of preferably 5.0-8.0 dl/g, more preferably 5.5-7.5 dl/g as determined in tetralin solution at 135xc2x0 C., and has an ethylene content [(C2xe2x80x2)EF] of preferably 25-35% by weight, more preferably 27-33% by weight.
When the intrinsic viscosity [xcex7]EP of the ethylene-propylene random copolymer portion of the second segment is less than 5.0 dl/g, a good result cannot be obtained in the balance of rigidity with impact resistance in some cases. When it exceeds 8.0 dl/g, hard spots tend to develop and a good result cannot be obtained in respect of surface quality in some cases. When the ethylene content [(C2xe2x80x2)EP] of the portion is less than 25% by weight or higher than 35% by weight, a good result cannot be obtained in respect of the impact resistance of the composition in some cases.
The ratio of the ethylene-propylene random copolymer portion (the second segment) to the propylene homopolymer portion (the first segment) (namely, the second segment/the first segment) by weight is preferably 8/92 to 35/65.
The crystalline propylene homopolymer used in the above-mentioned mixture (1B) of the crystalline ethylene-propylene block copolymer (1A) with the crystalline propylene homopolymer is a polymer which have similar physical properties to those of the propylene homopolymer portion of the first segment. Thus, it has a Q value of 3.0-5.0, preferably 3.5-4.5, which value is the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) determined by the gel permeation chromatography (GPC) method, an isotactic pentad fraction, calculated from its 13C-NMR, of preferably not less than 0.98, more preferably not less than 0.99, and an intrinsic viscosity [xcex7]p of preferably 0.7-1.1 dl/g, more preferably 0.8-1.0 dl/g as determined in tetralin solution at 135xc2x0 C.
When the Q value of the crystalline propylene homopolymer used in the mixture (1B) of the crystalline ethylene-propylene block copolymer (1A) with a crystalline propylene homopolymer is less than 3.0, the fluidity tends to be poor, and when it exceeds 5.0, an unfavorable result is obtained in the balance of rigidity with impact resistance in some cases. Further, when the isotactic pentad fraction is less than 0.98, the intended rigidity, heat resistance and the like are hardly attained in some cases. Further, when the intrinsic viscosity [xcex7]p is less than 0.7 dl/g, the impact resistance tends to be low, and when it exceeds 1.1 dl/g, the fluidity tends to be poor.
The crystalline polypropylene-based resin (1) can be produced by using a Ziegler-Natta catalyst system and/or a metallocene catalyst system according to a bulk polymerization method, a solution polymerization method, a slurry polymerization method, a gas phase polymerization method, or any desired combination of these polymerization methods.
When the ethylene-propylene block copolymer is used in applications wherein a high impact resistance is particularly required, the block copolymer is preferably a product obtained by polymerizing propylene in the first step to produce a crystalline propylene homopolymer portion of the first segment and then polymerizing ethylene and propylene in the second step to produce an ethylene-propylene random copolymer portion of the second segment.
In the thermoplastic resin composition of this invention, the content of the crystalline polypropylene-based resin (1) is preferably 55-75% by weight relative to the whole of the composition.
Description is given below of the elastomer (2) comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-xcex1-olefin random copolymer rubber used in this invention.
The vinyl aromatic compound-containing rubber (2A) referred to in this invention is a block copolymer composed of a vinyl aromatic compound polymer block and a conjugated diene-based polymer block wherein 80% or more, preferably 85% or more of the double bonds of its conjugated diene portion have been hydrogenated and it has a Q value, determined by the GPC method, of preferably not more than 2.5, more preferably not more than 2.3, has a vinyl aromatic compound content in the vinyl aromatic compound-containing rubber of preferably 10-20% by weight, more preferably 12-19% by weight, and has a melt flow rate (hereinafter referred to as xe2x80x9cMFRxe2x80x9d) (according to JIS-K-6758, 230xc2x0 C.) of preferably 1-15 g/10 min, more preferably 2-13 g/10 min.
The vinyl aromatic compound-containing rubber (2A) in this invention is a rubber which comprises an olefin-based copolymer rubber or conjugated diene rubber and a vinyl aromatic compound bonded to said rubber through polymerization, reaction, etc., and may be, for example, such block copolymers as styrene-ethylene-butene-styrene type rubber (SEBS), styrene-ethylene-propylene-styrene type rubber (SEPS), styrene-butadiene type rubber (SBR), styrene-butadiene-styrene type rubber (SBS) and styrene-isoprene-styrene type rubber (SIS) and further block copolymers resulting from hydrogenation of the rubber components thereof. Rubbers obtained by reacting a vinyl aromatic compound, such as styrene, to an ethylene-propylene-non-conjugated diene type rubber (EPDM) may also be favorably used.
When the vinyl aromatic compound content in the vinyl aromatic compound-containing rubber (2A) is, on the average, lower than 10% by weight or higher than 20% by weight, the affinity of the rubber to the crystalline polypropylene-based resin (1) tends to be low, and resultantly the impact resistance and the rigidity tend to decrease.
The ethylene-xcex1-olefin random copolymer rubber used in this invention is a random copolymer rubber comprising ethylene and an xcex1-olefin and is not particularly limited so long as it is such a rubber. The xcex1-olefin has 3 or more, preferably 3-12 carbon atoms and is, for example, propylene, butene, pentene, hexene, heptene, octene, decene, and the like, preferred thereof being propylene, butene, hexene and octene.
The random copolymer rubber is, for example, an ethylene-propylene random copolymer rubber, ethylene-butene random copolymer rubber, ethylene-hexene random copolymer rubber, ethylene-octene random copolymer rubber, and the like. Preferred examples thereof are an ethylene-octene random copolymer rubber (2B), ethylene-butene random copolymer rubber (2C) and ethylene-propylene random copolymer rubber (2D).
The ethylene-octene random copolymer rubber (2B) used in this invention has a Q value, determined by the GPC method, of preferably not more than 2.5, more preferably not more than 2.3, and has an octene content of 15-45% by weight, preferably 18-42% by weight. The ethylene-octene random copolymer rubber has a MFR (according to JIS-K-6758, 190xc2x0 C.) of preferably 1.0-15.0 g/10 min, more preferably 2-13 g/10 min.
When the Q value, determined by the GPC method, of the ethylene-octene random copolymer rubber (2B) exceeds 2.5, the rigidity tends to decrease in some cases. When the octene content in the ethylene-1-octene random copolymer rubber (2B) is less than 15% by weight, this is unfavorable in respect of the impact resistance; when it exceeds 45% by weight, a favorable result cannot be obtained in respect of the rigidity. When the MFR of the ethylene-octene random copolymer rubber (2B) exceeds 15 g/10 min, this is unfavorable in respect of the impact resistance; and when it is lower than 1.0 g/10 min, the dispersion of the rubber in the crystalline polypropylene-based resin (1) tends to be poor, leading to an unfavorable result in respect of the impact resistance.
The ethylene-1-butene random copolymer rubber (2C) used in this invention has a Q value, determined by the GPC method, of preferably not more than 2.7, more preferably not more than 2.5, and has a butene content of preferably 15-35% by weight, more preferably 17-33% by weight. The ethylene-butene random copolymer rubber (2C) has a MFR (according to JIS-k-6758, 190xc2x0 C.) of preferably 1-15 g/10 min, more preferably 2-13 g/10 min.
When the Q value, determined by the GPC method, of the ethylene-butene random copolymer rubber (2C) exceeds 2.7, the rigidity tends to decrease in some cases. When the butene content in the ethylene-butene random copolymer rubber (2C) is less than 15% by weight, this is unfavorable in respect of the impact resistance; when it exceeds 35% by weight, a favorable result cannot be obtained in respect of the rigidity. When the MFR of the ethylene-butene random copolymer rubber is lower than 1 g/10 min, this is unfavorable in respect of the rigidity and impact resistance; when it exceeds 15 g/10 min, the dispersion of the rubber in the crystalline polypropylene-based resin (1) tends to be poor, leading to an unfavorable result in respect of the impact resistance.
The ethylene-propylene random copolymer rubber (2D) has a Q value, determined by the GPC method, of preferably not more than 2.7, more preferably not more than 2.5, has a propylene content of 20-30% by weight, preferably 22-28% by weight, and has a MFR (according to JIS-K-6758, 190xc2x0 C.) of preferably 1-15 g/10 min, more preferably 2-13 g/10 min.
When the Q value, determined by the GPC method, of the ethylene-propylene random copolymer rubber (2D) exceeds 2.7, the rigidity tends to decrease. When the propylene content in the ethylene-propylene random copolymer rubber (2D) is lower than 20% by weight, this is unfavorable in respect of the impact resistance; when it exceeds 30% by weight, a favorable result cannot be obtained in respect of the rigidity in some cases. When the MFR of the ethylene-propylene random copolymer rubber (2D) is less than 1 g/10 min, this is unfavorable in respect of the rigidity and impact resistance; when it exceeds 15 g/10 min, the dispersion of the rubber in the crystalline polypropylene-based resin (1) tends to be poor, leading to an unfavorable result in respect of the impact resistance in some cases.
The ethylene-octene random copolymer rubber (2B), ethylene-butene random copolymer rubber (2C) and ethylene-propylene random copolymer rubber (2D) can be produced by copolymerizing ethylene with various xcex1-olefins with a catalyst system comprising a vanadium compound and an organoaluminum compound, Ziegler-Natta catalyst system or metallocene catalyst system through a solution polymerization method, slurry polymerization method, high pressure ionic polymerization method or gas phase polymerization method.
The content of the elastomer (2) comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-xcex1-olefin random copolymer rubber relative to the whole of the thermoplastic resin composition of this invention is 10-30% by weight. When the content of the elastomer is less than 10% by weight, the impact resistance tends to decrease unfavorably; when it exceeds 30% by weight, the rigidity and the heat resistance tend to decrease unfavorably.
In using the above-mentioned rubber components (2A)-(2D), the respective contents of the various rubbers constituting the elastomer relative to the whole of the composition are, preferably, 3-15% by weight for the vinyl aromatic compound-containing rubber (2A), 0-15% by weight for the ethylene-octene random copolymer (2B), 0-10% by weight for the ethylene-butene random copolymer (2C) and 0-10% by weight for the ethylene-propylene random copolymer (2D).
In using the above-mentioned rubber components (2A)-(2D), it is preferable that the resulting resin composition contains the ethylene-octene random copolymer (2B), and it is further preferable that the composition contains both the ethylene-octene random copolymer (2B) and the ethylene-butene random copolymer (2C).
In the thermoplastic resin composition of this invention, furthermore, it is preferable that the contents (% by weight) and weight fractions of the respective components satisfy the following expressions 1)-3).
(Xpp)+(Xst)+(XEOR)+(XEBR)+(XEPR)+(Xtalc)=100,xe2x80x83xe2x80x831)
0.20xe2x89xa6{[(YBC)xc3x97(YEP)+(Xst)+(XEOR)+(XEBR)+(XEPR)]/100}xe2x89xa60.30,xe2x80x83xe2x80x832)
and
0.1xe2x89xa6{(YBC)xc3x97(YEP)/[(YBC)xc3x97(YEP)+(Xst)+(XEOR)+(XEPR)+(XEPR)]},xe2x80x83xe2x80x833)
wherein (Xpp) is the content (% by weight) of the crystalline polypropylene, (Xst) is that of the vinyl aromatic compound-containing rubber (2A), (XEOR) is that of the ethylene-octene random copolymer rubber (2B), (XEBR) is that of the ethylene-butene random copolymer rubber (2C) and (XEPR) is that of the ethylene-propylene random copolymer rubber (2D); (YBC) is the content (% by weight) of the crystalline ethylene-propylene block copolymer (1A), (YEP) is the weight fraction (weight fraction being content (% by weight)/100) of the ethylene-propylene random copolymer portion which is the second segment in the crystalline ethylene-propylene block copolymer (1A), and (Xtalc) is the content (% by weight) of talc.
When the numerical value of [(YBC)xc3x97(YEP)+(Xst)+(XEOR)+(XEBR)+(XEPR)]/100 in the above expression (2) is less than 0.20, the impact resistance tends to decrease unfavorably; when it exceeds 0.30, the fluidity tends to decrease unfavorably. When the numerical value of (YBC)xc3x97(YEP)/[(YBC)xc3x97(YEP)+(Xst)+(XEOR)+(XEBR)+(XEFR)] in the relational expression (3) for the weight fractions of respective components of the thermoplastic resin composition of this invention is less than 0.1, the impact resistance tends to decrease unfavorably.
The MFR (according to JIS-K-6758, 230xc2x0 C.) of the thermoplastic resin composition of this invention is preferably not less than 35 g/10 min, because when it is less than 35 g/10 min, the fluidity tends to be poor, resulting in lowered moldability.
The talc used in this invention is a product obtained by pulverizing magnesium silicate hydrate. The crystal structure of its molecule assumes a three-layer structure of pyrophyllite type, and talc is composed of said layers piled one upon another. Particularly preferred are those in the form of plate obtained by finely grinding the crystals approximately to the extent of unit layers.
The average particle diameter of the talc used in this invention is not more than 3 xcexcm. When it is more than 3 xcexcm, the impact resistance of the thermoplastic resin composition of this invention tends to decrease greatly, and the appearance, such as gloss, also tends to be poor. The talc may be used as such without being treated; however, it may also be used after its surface has been treated, for the purpose of enhancing the interfacial adhesiveness to the crystalline polypropylene-based resin (1) and enhancing the dispersibility, with various known silane coupling agents, titanium-coupling agents, higher fatty acids, higher fatty acid esters, higher fatty acid amides, higher fatty acid salts or other surfactants.
The average particle diameter of talc herein means a fifty percent particle diameter D50 determined from the integral distribution curve of the undersize method obtained by subjecting a suspension of talc particles in a dispersion medium, such as water, alcohol or the like, to measurement by using a centrifugal sedimentation particle size distribution measuring apparatus.
The content of the talc used in this invention is 15-25% by weight relative to the whole of the thermoplastic resin composition. When the content of talc to be used is less than 15% by weight, the rigidity and the heat resistance tend to decrease, whereas when it exceeds 25% by weight, the impact resistance tends to decrease unfavorably and the appearance also tends to be poor.
The thermoplastic resin composition of this invention satisfies the following conditions (a)-(c). That is, at first,
(a) when the crystalline polypropylene-based resin (1) has been melt-kneaded with the elastomer (2) comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-a-olefin random copolymer rubber, it is necessary that the long period obtained by small angle X-ray scattering attributable to the vinyl aromatic compound-containing rubber is 12-24 nm.
The small angle X-ray scattering is, as described in known publications, for example, xe2x80x9cX-sen Kaisetsu no Tebiki (Guide to X-ray Diffraction), published by Rigaku Denki (K.K.), 1989 ed.)xe2x80x9d, scattering in a small angle region of 2{circle around (H)} of not more than several degrees, and the xe2x80x9clong periodxe2x80x9d refers to a periodic arrangement of crystalline portions and non-crystalline portions of approximately several ten to several hundred xc3x85. The long period attributable to the vinyl aromatic compound-containing rubber can be obtained by regarding diffraction peaks other than known diffraction peaks attributable to the crystalline polypropylene resin as attributable to the vinyl-aromatic compound-containing rubber.
The long period attributable to the vinyl-aromatic compound-containing rubber is preferably 12-23 nm. When it exceeds 24 nm, it greatly deviates from the long period of crystalline polypropylene-based resin, and resultantly the interfacial adhesive strength (interaction) between the elastomer phase and the crystalline polypropylene-based resin phase decreases.
(b) When the crystalline polypropylene-based resin (1) has been melt-kneaded with the elastomer comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-xcex1-olefin random copolymer rubber, it is necessary that elastomer particles which undergo micro phase separation to have the form of particle, and are present in the vicinity of the interface between particles of the elastomer and polypropylene as matrix, have a particle diameter of not more than 30 nm.
The state of the vicinity of the interface between particles of the elastomer and crystalline polypropylene resin as matrix and the state of micro phase separation of elastomer particles present in the vicinity of the interface can be observed by a transmission type electron microscope (TEM). The shape of the particles can be judged by visually observing or photographing the transmitted image, and the particle diameter can be obtained by calculation based on the magnification of the microscope.
The particle diameter of the elastomer particles which undergo micro phase separation to have the form of particle, and are present in the vicinity of the interface between particles of the elastomer and polypropylene as matrix, are preferably not more than 25 nm. When the elastomer which is present in the vicinity of the interface between particles of the elastomer and crystalline polypropylene resin as matrix and undergo micro phase separation is in the form of rod or plate, or when, though it is in the form of particle, its diameter exceeds 30 nm, the impact resistance of the thermoplastic resin composition is decreased, and a favorable result cannot be obtained.
Furthermore, it is necessary that (c) the difference between the glass transition point (Tg1) assigned to the crystalline propylene homopolymer portion of the crystalline polypropylene-based resin (1) and the glass transition point (Tg2) assigned to the crystalline homopolymer portion of a composition obtained by melt-kneading the crystalline polypropylene-based resin (1) with the elastomer (2) comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-xcex1-olefin random copolymer rubber and talc (3) (that is, xcex94Tg=Tg1xe2x88x92Tg2) is 4.0-7.0xc2x0 C.
The glass transition point herein referred to is the glass transition point in non-crystalline polymer, which is the temperature at which the non-crystalline polymer changes from the glass state to the rubber state (or conversely) and can be determined from the absorption peak obtained by the measurement of temperature dispersion of loss modulus. In the case of the crystalline polypropylene-based resin (1), in most instances only one glass transition point assigned to the crystalline propylene homopolymer portion is observed, which is designated Tg1. In the case of a polymer obtained by melt-kneading a mixture of a crystalline polypropylene-based resin (1), an elastomer (2) comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-xcex1-olefin random copolymer rubber and talc (3), two glass transition points, that is, the glass transition point assigned to the crystalline propylene homopolymer portion and the glass transition point assigned to the elastomer portion are observed; of the two points, the glass transition point assigned to the crystalline propylene homopolymer portion is designated Tg2. From these two glass transition points, the difference (xcex94Tg=Tg1xe2x88x92Tg2) between the glass transition points assigned to the crystalline propylene homopolymer portion can be obtained.
When the difference (xcex94Tg=Tg1xe2x88x92Tg2) in the glass transition point assigned to the crystalline propylene homopolymer portion is less than 4.0, the affinity between the crystalline polypropylene resin (1) and the elastomer (2) comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-xcex1-olefin random copolymer rubber tends to decrease greatly, resulting in the decrease of the impact resistance of the thermoplastic resin composition of this invention.
When the difference (xcex94Tg=Tg1xe2x88x92Tg2) in the glass transition point assigned to the crystalline propylene homopolymer portion exceeds 7.0xc2x0 C., the affinity tends to be in excess, resulting unfavorably in the decrease of the rigidity and the heat resistance of the thermoplastic resin composition of this invention, and the favorable result can not be obtained.
The thermoplastic resin composition of this invention can be produced by using a kneader, such as a single screw extruder, a twin screw extruder, a Banbury mixer, a hot roll or the like. The addition to and mixing in the kneader of the respective components may be conducted at the same time or may be conducted in portions. The operations may be conducted, for example, according to the following methods, but they are not limited thereto.
(Method 1)
A method which comprises kneading the crystalline polypropylene-based resin (1) with the talc (3) and then adding thereto the elastomer (2) (hereinafter abbreviated as xe2x80x9celastomerxe2x80x9d) comprising a vinyl aromatic compound-containing rubber or comprising a vinyl aromatic compound-containing rubber and an ethylene-xcex1-olefin random copolymer rubber.
(Method 2)
A method which comprises kneading the crystalline polypropylene-based resin (1) with talc in a high talc concentration beforehand to prepare a master batch and then separately kneading the master batch while diluting it with the crystalline polypropylene-based resin (1) and the elastomer (2), etc.
(Method 3)
A method which comprises kneading the crystalline polypropylene-based resin (1) with the elastomer (2), and then adding the talc (3) thereto and kneading the resulting mixture.
(Method 4)
A method which comprises kneading the crystalline polypropylene-based resin (1) with the elastomer (2) in a high elastomer concentration before-hand to prepare a master batch, and then adding thereto the crystalline polypropylene-based resin (1) and the talc (3) and kneading the resulting mixture.
(Method 5)
A method which comprises respectively kneading the crystalline polypropylene-based resin (1) with the talc (3) and the crystalline polypropylene-based resin (1) with the elastomer (2) beforehand and finally kneading them together.
The temperature required for the kneading is 170-250xc2x0 C., preferably 190-230xc2x0 C. The time necessary for the kneading is 1-20 minutes, preferably 3-15 minutes.
In these kneaders, in addition to these basic components, there can be compounded, as desired according to the objects of this invention, additives, such as an antioxidant, ultraviolet absorber, lubricant, pigment, antistatic agent, copper inhibitor, flame retardant, neutralizing agent, foaming agent, plasticizer, nucleating agent, foam inhibitor, cross-linking agent and the like.
The thermoplastic resin composition of this invention can be used for producing moldings of various shapes by the conventionally used injection molding method. The injection moldings thus obtained are suitably used particularly as automobile interior and exterior trim parts, such as a door trim, pillar, instrumental panel, bumper, and the like.